The present invention relates generally to milling machines, and more particularly to an automated quill drive assembly that is adapted for retrofitted use on a conventional milling machine to drive Z-axis movement of the quill in response to control from a conventional computer numerical control (xe2x80x9cCNCxe2x80x9d) controller or the like.
A conventional milling machine, such as a knee mill, includes a table on which a work piece can be supported, and a quill that supports a tool for movement toward and away from the table for milling the work piece. Typically, the table is adjustable within a horizontal plane from side-to-side and from front-to-back relative to the quill. Lateral side-to-side adjustment is considered X-axis adjustment, and front-to-back adjustment is referenced as Y-axis adjustment As such, the position of a work piece can be changed in two planes, and the quill moves vertically along a Z-axis such that three-axis adjustment of the tool relative to the work piece is possible.
Although many milling machines are manual, in the sense that adjustment of the table and movement of the quill is manually achieved, improvements in the art have resulted in fully automatic machines in which X-axis, Y-axis and Z-axis movement of the table and/or quill are computer controlled and carried out by stepper or servo motors. These automatic machines provide many advantages over manual machines, especially with respect to the reproducibility of milling operations performed with such milling machines. However, automatic machines lack the versatility of manual designs, and cost significantly more to purchase and use.
Automated drive assemblies are known that can be retrofitted on an existing milling machine to automate the X-axis and Y-axis movement of the table and the Z-axis movement of the quill. Typically, a CNC controller is installed on the machine at the same time as one or more of these drive assemblies such that the drive assemblies are capable of being operated automatically subsequent to installation.
A conventional Z-axis or quill drive assembly broadly includes a housing supported on the quill head of the machine, a stepper or servo motor supported on the housing and operatively connected to a conventional CNC controller, and a transmission that is supported on the housing and connected between the motor and the quill to transmit the motor drive to the quill so that when the motor is operated, the quill is moved between the retracted and extended positions. The housing is secured to the head at three points, one of which is defined by a lower casting lug of the quill head normally used to support a depth stop screw. The second and third points of attachment of the housing are defined by a pair of vertically spaced tramming bolts provided along the right front side of the quill head.
In the conventional automated quill drive assembly, the position of the quill is continuously monitored by providing feedback from the motor to the CNC controller indicative of the position or operation of the motor. In addition, limit switches are sometimes employed to provide a positive signal when the quill is moved to either the fully retracted or fully extended limit position. In this way, the CNC controller is able to control operation of the motor to accurately position and reposition the quill along the Z-axis during milling operations.
Although conventional automated quill drive assemblies do allow a manual milling machine to be retrofitted for automatic operation, further improvements would be advantageous. For example, because the housing of a conventional assembly is mounted to two of the tramming bolts on the quill head, the housing must be loosened in order to tram the head. Such added complexity makes tramming of the quill head difficult and time consuming.
Further, although three mounting points are provided for the housing of a conventional quill drive assembly, two of the points are in line with one another vertically, and the third point is spaced laterally from the other two by only 1 to 2 inches. As a result, the motor can twist or wind up when milling a heavy cut, reducing the accuracy of the machine, and increasing wear on the quill.
Another feature of the conventional quill drive assembly subject to improvement is the source of feedback provided to the CNC controller which allows the position of the quill to be continuously monitored and controlled during automatic operation. Because the conventional assembly monitors quill movement indirectly by sensing motor movement or operation, the CNC controller can only monitor the quill position when the quill is operated by the motor, or when manual quill movement is transmitted back to the motor. As such, manual operation of the quill is either frustrated or must be performed without the benefit of feedback to the CNC controller. When manual operation is performed without such feedback, depth control and repeatability become difficult to achieve.
It is an object of the present invention to provide an automated quill drive assembly for use with a milling machine, wherein the presence of the quill drive assembly does not prevent or impede tramming of the quill head, and permits quick conversion between automated and manual operation of the machine.
It is another object of the invention to provide an automated quill drive assembly in which the position of the quill is sensed directly, rather than indirectly through a motor, allowing the position of the quill to be continuously displayed by a CNC controller regardless of whether quill movement is achieved manually or automatically.
Yet another object of the invention is to provide a quill drive assembly that can be rigidly secured to the quill head of a conventional milling machine at three laterally spaced points to fix the motor and other components of the assembly against flexing under the stress of heavy milling operations.
In accordance with these and other objects evident from the following description of a preferred embodiment of the invention, an automated quill drive assembly is provided that is specially adapted to be retrofit on a milling machine of the category having a frame presenting a quill head and a quill supported on the head for rotation and for relative shiftable movement along a linear axis between retracted and extended positions. Typically, the quill head of the milling machine includes a centrally disposed lower lug, a quill feed engagement control lever boss located above and spaced to one side of the lug, and a transmission cover boss located above and spaced to a side of the lug opposite the quill feed engagement control lever boss. Further, the milling machine includes a manually actuated lever supported on the head and operatively connected to the quill for moving the quill between the retracted and extended positions.
The automated quill drive assembly includes a housing adapted to be mounted to the casting lug, the quill feed engagement control lever boss, and the transmission cover opening, a motor supported on the housing, and a transmission supported on the housing and being adapted for connection between the motor and the quill for transmitting drive to the quill to move it between the retracted and extended positions. A controller, such as a CNC controller, is preferably employed with the quill drive assembly for controlling automatic movement of the quill, as well as for controlling other operations of the milling machine, e.g. X-axis and Y-axis drive assemblies of conventional construction.
In accordance with another aspect of the present invention, the automated quill drive assembly includes a housing, a motor, a transmission connected between the motor and the quill for transmitting drive to the quill, and a sensor for continuously sensing the position of the quill as the quill is moved between the retracted and extended positions. The sensor provides an output signal indicative of the position of the quill for both manual and automated movement, and the signal can be supplied to a conventional controller to provide a display of the position of the quill as it is moved.
By providing a quill drive assembly in accordance with the present invention, numerous advantages are realized. For example, by providing an automated quill drive assembly that is mounted to the quill head at a first point of attachment disposed in a vertical plane including the longitudinal axis of the quill, and at second and third points of attachment disposed on opposite sides of the vertical plane, the assembly is rigidly secured in place on the quill head, fixing the motor and other assembly components against flexing when a heavy cut is made or when the quill drive assembly is otherwise placed under stress.
In addition, because the quill drive assembly of the present invention does not employ the existing tramming bolts as mounting points, it is not necessary to loosen the quill drive assembly or to undertake other cumbersome steps when tramming the head of the milling machine as may be required for certain operations.
Another advantage achieved by the present invention resides in the use of a sensor that directly senses quill movement rather than motor movement, enabling the controller to provide an indication of quill position during both automated and manual quill movement. This allows an operator to control the depth of the quill and to repeat milling operations with extreme accuracy, even when performing such operations manually.